Urea concentration identifying system, method for indentifying urea concentration and automobile exhaust gas reducing system using same, and method for reducing automobile exhaust gas

ABSTRACT

The concentration of the urea of a urea solution is identified accurately and immediately. A pulse voltage is applied for a predetermined time to a urea concentration identifying sensor heater including a heater and an identifying liquid temperature sensor provided in the vicinity of the heater, a urea solution to be identified is heated by the heater, and the concentration of the urea is identified with a voltage output difference V 0  corresponding to a temperature difference between an initial temperature and a peak temperature in the identifying liquid temperature sensor.

TECHNICAL FIELD

The present invention relates to an apparatus and method for identifyingthe concentration of the urea of a urea solution, and an apparatus andmethod for reducing the exhaust gas of a car using the apparatus andmethod.

BACKGROUND ART

Conventionally, the exhaust gas of a car contains pollutants such asunburned hydrocarbon (HC), an NOx gas and an SOx gas. In order to reducethe pollutants, therefore, Sulfur (S) in a gasoline or light oil isremoved for the Sox or unburned Hydrocarbon (HC) is burned by acatalyst, for example.

More specifically, as shown in FIG. 13, a car system 100 takes air inthrough an automatic element (filter) 102 and feeds the air into anengine 106 through an airflow sensor 104. Moreover, the car system 100feeds a fuel in a fuel tank 108 into the engine 106 through a fuel pump110.

Based on the result of the detection of an A/F sensor 112, the injectionof the fuel in the engine 106 is controlled by a fuel injection controldevice 114 in order to have a predetermined theoretical air fuel ratio.

For an exhaust gas fed from the engine 106, hydrocarbon (HC) in theexhaust gas is burned by a catalytic device 116 and is then dischargedas the exhaust gas through an oxygen concentration sensor 118.

In consideration of the influence of the NOx in the exhaust gas on anenvironment, recently, there has been proposed a method of supplying aurea solution to the catalytic device 116, thereby reducing the NOx tobe non-toxic as an N₂ gas in order to decrease the NOx in the exhaustgas discharged from the fuel of a car, for example, a gasoline or lightoil.

More specifically, as shown in FIG. 13, the car system 100 has such astructure as to supply a urea solution to the upstream side of thecatalytic device 116 through a urea solution supplying mechanism 130constituted by a urea solution tank 132 for storing a urea solution, aurea pump 134 and a urea spraying device 136 for spraying the ureasolution fed from the urea pump 134 onto the upstream side of thecatalytic device 116.

In such a car system, it is suitable that 32.5% by weight of urea and67.5% by weight of H₂O should be set in order to efficiently generate areducing reaction at the upstream side of the catalytic device 116without causing the urea solution to cake, for example.

For this reason, conventionally, NOx sensors 140 and 142 have beenprovided at the upstream and downstream sides of the catalytic device116 respectively to measure the concentration of NOx in order to decidewhether or not the concentration of a urea sprayed onto the upstreamside of the catalytic device 116 is constant.

However, the NOx sensors 140 and 142 measure the concentration of theurea as a result of the reducing rate of NOx. For this reason, it isimpossible to previously identify the concentration of the urea which iscontained in the urea solution tank 132 or is sprayed. Moreover, the NOxsensors 140 and 142 do not have very high sensitivities.

The present inventors have already proposed a fluid identifying methodin Japanese Laid-Open Patent Publication No. 11-153561 (particularly seeparagraphs [0042] to [0049]). This method is to cause a heating memberto generate heat by carrying electricity, heating a temperature detectorthrough the heat generation, thermally influencing a heat transfer fromthe heating member to the temperature detector through a fluid to beidentified, and distinguishing the type of the identified fluid based onan electrical output corresponding to the electric resistance of thetemperature detector, thereby periodically carrying the electricity tothe heating member.

In the fluid identifying method, however, it is necessary toperiodically carry the electricity to the heating member (in amultipulse). For this reason, a long time is required for theidentification so that it is hard to identify a fluid instantaneously.In this method, moreover, it is possible to identify a fluid based on acentral value for substances having very different properties such aswater, air and oil. However, it is hard to identify the concentration ofthe urea of the urea solution accurately and immediately.

In consideration of such circumstances, it is an object of the presentinvention to provide an apparatus and method for identifying theconcentration of the urea of a urea solution which can identify theconcentration of the urea of the urea solution accurately andimmediately.

Moreover, it is an object of the present invention to provide anapparatus and method for reducing the exhaust gas of a car using theapparatus and method for identifying the concentration of the urea of aurea solution which can efficiently reduce the exhaust gas and canenhance a mileage.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the problems and to attainthe objects in the prior art described above, and provides an apparatusfor identifying a concentration of a urea of a urea solution,comprising:

a urea concentration identifying chamber for causing an identified ureasolution introduced into a urea concentration identifying apparatus bodyto stay temporarily;

a urea concentration identifying sensor heater provided in the ureaconcentration identifying chamber; and

a liquid temperature sensor provided in the urea concentrationidentifying chamber apart from the urea concentration identifying sensorheater at a constant interval;

the urea concentration identifying sensor heater including a heater andan identifying liquid temperature sensor provided in the vicinity of theheater, and

the apparatus further comprising an identification control portion forapplying a pulse voltage to the urea concentration identifying sensorheater for a predetermined time, heating the identified urea solutionstaying temporarily in the urea concentration identifying chamber by theheater and identifying the concentration of the urea with a voltageoutput difference V0 corresponding to a temperature difference betweenan initial temperature and a peak temperature in the identifying liquidtemperature sensor.

Moreover, the present invention provides a method for identifying aconcentration of a urea of a urea solution, comprising the steps of:

applying a pulse voltage for a predetermined time to a ureaconcentration identifying sensor heater including a heater and anidentifying liquid temperature sensor provided in the vicinity of theheater;

heating an identified urea solution by the heater; and

identifying the concentration of the urea with a voltage outputdifference V0 corresponding to a temperature difference between aninitial temperature and a peak temperature in the identifying liquidtemperature sensor.

By such a structure, it is sufficient that the pulse voltage is appliedfor the predetermined time. Consequently, it is possible to identify theconcentration of the urea of the urea solution accurately andimmediately through heating for a short time.

More specifically, there are utilized the correlation of the kineticviscosity of the urea solution with a sensor output, a naturalconvection, and furthermore, an applied voltage having one pulse.Therefore, it is possible to identify the concentration of the urea ofthe urea solution accurately and immediately.

Furthermore, the present invention is characterized in that the voltageoutput difference V0 is equal to a voltage difference between an averageinitial voltage V1 obtained by sampling an initial voltage beforeapplication of the pulse voltage at a predetermined number of times andan average peak voltage V2 obtained by sampling a peak voltage after theapplication of the pulse voltage at a predetermined number of times,that is,V 0=V 2−V 1.

By such a structure, it is possible to accurately obtain the voltageoutput difference V0 based on the average value of the sampling at thepredetermined number of times for the applied voltage having one pulse.Consequently, it is possible to identify the concentration of the ureaof the urea solution accurately and immediately.

In addition, the present invention provides the apparatus foridentifying a concentration of a urea of a-urea solution, wherein theidentification control portion identifies a concentration of a urea of aurea solution with the voltage output difference V0 obtained for theidentified urea solution based on calibration curve data to be acorrelation of a voltage output difference with a temperature for apredetermined reference urea solution prestored in the identificationcontrol portion.

Moreover, the present invention provides the method for identifying aconcentration of a urea of a urea solution, wherein a concentration of aurea of a urea solution is identified with the voltage output differenceV0 obtained for the identified urea solution based on calibration curvedata to be a correlation of a voltage output difference with atemperature for a predetermined reference urea solution which isprestored.

By such a structure, the concentration of the urea of the urea solutionis identified with the voltage output difference V0 obtained for theidentified urea solution based on the calibration curve data, which iscorrelated with the voltage output difference with the temperature forthe predetermined reference urea solution which is prestored. Therefore,it is possible to identify the concentration of the urea of the ureasolution more accurately and immediately.

Furthermore, the present invention provides the apparatus foridentifying a concentration of a urea of a urea solution, wherein theidentification control portion correlates a liquid type voltage outputVout for the voltage output difference V0 at a measuring temperature ofthe identified urea solution with an output voltage for a voltage outputdifference at a measuring temperature for a predetermined thresholdreference urea solution and thus carries out a correction.

In addition, the present invention provides the method for identifying aconcentration of a urea of a urea solution, wherein a liquid typevoltage output Vout for the voltage output difference V0 at a measuringtemperature of the identified urea solution is correlated with an outputvoltage for a voltage output difference at a measuring temperature for apredetermined threshold reference urea solution and is thus corrected.

By such a structure, the liquid type voltage output Vout for the voltageoutput difference V0 at the measuring temperature of the identified ureasolution is correlated with the output voltage for the voltage outputdifference at the measuring temperature for the predetermined thresholdreference urea solution and is thus corrected. Consequently, it ispossible to eliminate the influence of the temperature on the voltageoutput difference V0, thereby giving the correlation of the liquid typevoltage output Vout with the properties of the urea solution moreaccurately. Thus, it is possible to identify the concentration of theurea of the urea solution further accurately and immediately.

Moreover, the present invention is characterized in that the ureaconcentration identifying sensor heater is a laminated ureaconcentration identifying sensor heater in which a heater and anidentifying liquid temperature sensor are laminated through aninsulating layer.

By such a structure, a mechanism portion for carrying out a mechanicaloperation is not present. Therefore, an operation failure is not causedby a deterioration with the passage of time, foreign matters in the ureasolution or the like. Thus, it is possible to identify the concentrationof the urea of the urea solution accurately and immediately.

In addition, the sensor portion can be constituted to be verysmall-sized. Consequently, it is possible to identify the concentrationof the urea of the urea solution accurately with a very excellentthermal responsiveness.

Furthermore, the present invention is characterized in that the heaterand the identifying liquid temperature sensor in the urea concentrationidentifying sensor heater are constituted to come in contact with theidentified urea solution through a metallic fin, respectively.

By such a structure, the heater and the identifying liquid temperaturesensor in the urea concentration identifying sensor heater do notdirectly come in contact with the identified urea solution. Therefore,an operation failure is not caused by a deterioration with the passageof time, foreign matters in the urea solution or the like. Thus, it ispossible to identify the concentration of the urea of the urea solutionaccurately and immediately.

Moreover, the present invention is characterized in that the liquidtemperature sensor is constituted to come in contact with the identifiedurea solution through the metallic fin.

By such a structure, the liquid temperature sensor does not directlycome in contact with the identified urea solution. Therefore, anoperation failure is not caused by, a deterioration with the passage oftime, foreign matters in the urea solution or the like. Thus, it ispossible to identify the concentration of the urea of the urea solutionaccurately and immediately.

In addition, the present invention provides an apparatus for reducing anexhaust gas of a car, comprising

a urea solution supplying mechanism for supplying a urea solution to anupstream side of a catalytic device,

wherein the urea solution supplying mechanism is constituted by a ureasolution tank for storing the urea solution, a urea pump and a ureaspraying device for spraying the urea solution fed from the urea pump tothe upstream side of the catalytic device, and

any of the apparatuses for identifying a concentration of a urea of aurea solution described above is provided in the urea tank or on anupstream side or a downstream side of the urea pump.

Furthermore, the present invention provides a method for reducing anexhaust gas of a car, comprising the steps of supplying a urea solutionto an upstream side of a catalytic device through a urea solutionsupplying mechanism constituted by a urea solution tank for storing theurea solution, a urea pump and a urea spraying device for spraying theurea solution fed from the urea pump onto the upstream side of thecatalytic device, and

identifying a concentration of a urea of the urea solution in the ureatank or on an upstream side or a downstream side of the urea pump byusing any of the methods for identifying a concentration of a urea of aurea solution described above.

By such a structure, it enables to accurately and immediately decide theamount of urea concentration, for example, whether or not 32.5% byweight of urea and 67.5% by weight of H₂O are set in order toefficiently generate a reducing reaction at the upstream side of thecatalytic device 116 without causing the urea solution to cake.

Accordingly, the urea of the urea solution in the urea tank can bemaintained to have a predetermined concentration. Consequently, NOx inthe exhaust gas can be greatly decreased by a reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view showing an example of an apparatus foridentifying the concentration of the urea of a urea solution accordingto the present invention, FIG. 2 is a sectional view taken along an A-Aline in FIG. 1,

FIG. 3 is a right side view of FIG. 1,

FIG. 4 is a left side view of FIG. 1,

FIG. 5 is a partially enlarged sectional view showing a state in which aurea concentration identifying sensor is attached in FIG. 2,

FIG. 6 is a sectional view showing the urea concentration identifyingsensor,

FIG. 7 is a partially enlarged exploded perspective view showing a statein which the thin film chip portions of the urea concentrationidentifying sensor are laminated,

FIG. 8 is a schematic diagram showing the structure of a circuitaccording to the example of the apparatus for identifying theconcentration of the urea of a urea solution according to the presentinvention,

FIG. 9 is a graph showing a relationship between a time and a voltage,illustrating a method for identifying the concentration of a urea usingthe apparatus for identifying the concentration of the urea of a ureasolution according to the present invention,

FIG. 10 is a graph showing a calibration curve, illustrating the methodfor identifying the concentration of a urea using the apparatus foridentifying the concentration of the urea of a urea solution accordingto the present invention,

FIG. 11 is a graph showing an output correcting method in the method foridentifying the concentration of a urea using the apparatus foridentifying the concentration of the urea of a urea solution accordingto the present invention,

FIG. 12 is the same schematic diagram as FIG. 13, illustrating anexample in which an apparatus 10 for identifying the concentration ofthe urea of a urea solution according to the present invention isapplied to a car system, and

FIG. 13 is a schematic diagram showing a conventional car system.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments (examples) of the present invention will be described belowin more detail with reference to the drawings.

As shown in FIGS. 1 and 2, an apparatus 10 for identifying theconcentration of the urea of a urea solution according to the presentinvention comprises a urea concentration identifying apparatus body 12,and a first passage 14 and a second passage 16 which are formed in theurea concentration identifying apparatus body 12.

As shown in an arrow of FIG. 1, a urea solution to be identified whichflows from a urea solution inlet 18 into the first passage 14 passesthrough an intermediate chamber 56. Then, the identified urea solutionpasses through the intermediate chamber 56, and thereafter, enters thesecond passage 16 to temporarily stay in a urea concentrationidentifying chamber 20.

The urea concentration identifying chamber 20 is provided with anopening portion 22 for a urea concentration identifying sensor takingthe shape of an almost truck in an upper part thereof.

As shown in FIG. 2, a urea concentration identifying sensor 24 isattached to the opening portion 22 for the urea concentrationidentifying sensor.

As shown in FIG. 5, the urea concentration identifying sensor 24includes a urea concentration identifying sensor heater 25 and a liquidtemperature sensor 28 provided apart from the urea concentrationidentifying sensor heater 25 at a constant interval. Then, the ureaconcentration identifying sensor heater 25 and the liquid temperaturesensor 28 are formed integrally by a mold resin 30.

As shown in FIG. 6, moreover, the urea concentration identifying sensorheater 25 includes a lead electrode 32 and a thin film chip portion 34.Moreover, the urea concentration identifying sensor heater 25 isprovided with a metallic fin 36 protruded into the urea concentrationidentifying chamber 20 to directly come in contact with the identifiedurea solution through the opening portion 22 for the urea concentrationidentifying sensor from the mold resin 30. Then, the lead electrode 32,the thin film chip portion 34 and the fin 36 are mutually connectedelectrically through a bonding wire 38.

On the other hand, the liquid temperatures sensor 28 also has the samestructure as that of the urea concentration identifying sensor heater25, and includes the lead electrode 32, the thin film chip portion 34,the fin 36 and the bonding wire 38 respectively.

As shown in FIG. 7, the thin film chip portion 34 is constituted by athin film-shaped chip in which a substrate 40 formed of Al₂O₃, atemperature sensor (temperature detector) 42 formed of PT, an interlayerinsulating film 44 formed of Sio₂, a heater (heating member) 46 formedof TaSiO₂, a heating member electrode 48 formed of Ni, a protective film50 formed of SiO₂, and an electrode pad 52 formed of Ti/Au are providedin order, for example.

While the thin film chip portion 34 of the liquid temperature sensor 28also has the same structure, it is so constituted as not to cause theheater (heating member) 46 to act but to cause only the temperaturesensor (temperature detector) 42 to act.

After the liquid type of the identified urea solution is identified bythe urea concentration identifying sensor 24, the identified ureasolution is discharged from the urea concentration identifying chamber20 to an outside through a urea solution discharge port 54.

In FIGS. 1 and 2, moreover, a circuit boardmember connected to the ureaconcentration identifying sensor 24 and a lid member for covering thecircuit board member are not shown.

The apparatus 10 for identifying the concentration of the urea of a ureasolution according to the present invention has the structure of acircuit shown in FIG. 8.

In FIG. 8, an identifying liquid temperature sensor 26 of the ureaconcentration identifying sensor heater 25 and the liquid temperaturesensor 28 in the urea concentration identifying sensor 24 are connectedto each other through two resistors 64 and 66, thereby constituting abridge circuit 68. The output of the bridge circuit 68 is connected tothe input of an amplifier 70, and the output of the amplifier 70 isconnected to the input of a computer 72 constituting an identificationcontrol portion.

Moreover, the applied voltage of a heater 74 of the urea concentrationidentifying sensor heater 25 is controlled under the control of thecomputer 72.

In the apparatus 10 for identifying the concentration of the urea of aurea solution which has such a structure, thus, the concentration of theurea of the urea solution is identified in the following manner.

First of all, the identified urea solution is caused to flow from theurea solution inlet 18 of the first passage 14 of the apparatus 10 foridentifying the concentration of the urea of a urea solution and iscaused to stay temporarily in the urea concentration identifying chamber20 of the second passage 16.

As shown in FIGS. 8 and 9, a pulse voltage P is applied to the heater 74of the urea concentration identifying sensor heater 25 under the controlof the computer 72 for a predetermined time, that is, four seconds inthe present example, and a change in the temperature of the analogoutput of a sensing portion, that is, the sensor bridge circuit 68 shownin FIG. 8 is measured.

More specifically, as shown in FIG. 9, the voltage difference of thesensor bridge circuit 68 is sampled at a predetermined number of times,for example, 256 times in the present example for one second before thepulse voltage P is applied to the heater 74 of the urea concentrationidentifying sensor heater 25, and an average value thereof is set to bean average initial voltage V1. The value of the average initial voltageV1 corresponds to the initial temperature of the identifying liquidtemperature sensor 26.

As shown in FIG. 9, the predetermined pulse voltage P, that is, avoltage of 10V in the present example is applied to the heater 74 of theurea concentration identifying sensor heater 25 for four seconds.Subsequently, a value obtained by sampling a peak voltage at apredetermined number of times, for example, 256 times in the presentexample for one second after a predetermined time, for example, 3seconds in the present example is set to be an average peak voltage V2.The average peak voltage V2 corresponds to the peak temperature of theidentifying liquid temperature sensor 26.

A voltage output difference V0 is obtained from a voltage differencebetween the average initial voltage V1 and the average peak voltage V2,that is,V 0=V 2−V 1.

By such a method, as shown in FIG. 10, calibration curve data to be thecorrelation of a voltage output difference with a temperature arepreviously obtained for a predetermined reference urea solution, thatis, 0% by weight of urea, 40% by weight of urea and 20% by weight ofurea in the present example, and are stored in the computer 72constituting the identification control portion.

Based on the calibration curve data, a proportional calculation iscarried out in the computer 72 and the concentration of the urea of theurea solution is identified with the voltage output difference V0obtained for the identified urea solution.

More specifically, as shown in FIG. 11, a liquid type voltage outputVout for the voltage output difference V0 at a measuring temperature Tof the identified urea solution is correlated with an output voltage fora voltage output difference at a measuring temperature for apredetermined threshold reference urea solution (20% by weight of ureaand 40% by weight of urea in the present example) and is thus corrected.

In other words, as shown in FIG. 11(A), a voltage output differenceV0−20 of 20% by weight of urea, a voltage output difference V0−40 of 40%by weight of urea and a voltage output difference V0−S of the identifiedurea solution are obtained at the temperature T based on the calibrationcurve data.

As shown in FIG. 11(B), the liquid type voltage output Vout of theidentified urea solution is obtained by setting the liquid type outputof the threshold reference urea solution, so that a correlation with theproperties of the urea can be acquired. In this case to have apredetermined voltage, that is, by setting the liquid type output of 40%by weight of urea to be 3.5V and the liquid type output of 20% by weightof urea to be 0.5V in the present example.

The liquid type voltage output Vout of the identified urea solution ispreviously compared with data stored in the computer 72 based on thecalibration curve data. Consequently, it is possible to identify theconcentration of the urea of the urea solution accurately andimmediately (instantaneously).

The method for identifying the concentration of the urea of a ureasolution described above utilizes a natural convection and a principlein which the kinetic viscosity of the urea and the sensor output have acorrelation.

FIG. 12 is the same schematic diagram as FIG. 13, illustrating anexample in which the apparatus 10 for identifying the concentration ofthe urea of a urea solution having such a structure is applied to a carsystem.

The same components as those in FIG. 13 have the same reference numeralsand detailed description thereof will be omitted.

In a car system 100, the apparatus 10 for identifying the concentrationof the urea of a urea solution is provided in a urea solution tank 132or on the upstream side of a urea pump 134.

The apparatus 10 for identifying the concentration of the urea of a ureasolution identifies the concentration of the urea of the urea solutionin the urea solution tank 132 or on the upstream or downstream side ofthe urea pump 134 (the case of the upstream side will be described inthe present example for convenience of explanation) and sets theconcentration of the urea to be sprayed onto the upstream side of acatalytic device 116 into a constant state, for example, 32.5% by weightof urea and 67.5% by weight of H₂O in order to efficiently generate areducing reaction at the upstream side of the catalytic device 116without causing the urea solution to cake.

Accordingly, the urea of the urea solution in the urea tank can bemaintained to have a predetermined concentration. Therefore, it ispossible to greatly decrease NOx in an exhaust gas by a reduction.

While the preferred examples of the present invention have beendescribed above, the present invention is not restricted thereto butvarious changes can be made without departing from the objects of thepresent invention, for example, a pulse voltage P, the number ofsampling operations and the like can be changed properly.

EFFECT OF THE INVENTION

According to the present invention, it is sufficient that a pulsevoltage is applied for a predetermined time. Consequently, it ispossible to identify the concentration of the urea of a urea solutionaccurately and immediately through heating for a short time.

More specifically, there are utilized the correlation of the kineticviscosity of the urea solution with a sensor output, a naturalconvection, and furthermore, an applied voltage having one pulse.Therefore, it is possible to identify the concentration of the urea ofthe urea solution accurately and immediately.

According to the present invention, moreover, it is possible toaccurately obtain a voltage output difference V0 based on the averagevalue of sampling at a predetermined number of times for the appliedvoltage having one pulse. Consequently, it is possible to identify theconcentration of the urea of the urea solution accurately andimmediately.

According to the present invention, furthermore, the concentration ofthe urea of the urea solution is identified with the voltage outputdifference V0 obtained for the identified urea solution based oncalibration curve data to be the correlation of a voltage outputdifference with a temperature for a predetermined reference ureasolution which is prestored. Therefore, it is possible to identify theconcentration of the urea of the urea solution more accurately andimmediately.

According to the present invention, moreover, a liquid type voltageoutput Vout for the voltage output difference V0 at the measuringtemperature of the identified urea solution is corrected to becorrelated with the output voltage for the voltage output difference atthe measuring temperature for a predetermined threshold reference ureasolution. Consequently, it is possible to eliminate the influence of thetemperature on the voltage output difference V0, thereby giving thecorrelation of the liquid type voltage output Vout with the propertiesof the urea solution more accurately. Thus, it is possible to identifythe concentration of the urea of the urea solution further accuratelyand immediately.

According to the present invention, furthermore, a mechanism portion forcarrying out a mechanical operation is not present. Therefore, anoperation failure is not caused by a deterioration with the passage oftime, foreign matters in the urea solution or the like. Thus, it ispossible to identify the concentration of the urea of the urea solutionaccurately and immediately.

In addition, the sensor portion can be constituted to be verysmall-sized. Consequently, it is possible to identify the concentrationof the urea of the urea solution accurately with a very excellentthermal responsiveness.

According to the present invention, moreover, the heater of the ureaconcentration identifying sensor heater, the identifying liquidtemperature sensor and the liquid temperature sensor do not directlycome in contact with the identified urea solution. Therefore, anoperation failure is not caused by a deterioration with the passage oftime, foreign matters in the urea solution or the like. Thus, it ispossible to identify the concentration of the urea of the urea solutionaccurately and immediately.

According to the present invention, furthermore, it is possible toaccurately and immediately decide whether or not 32.5% by weight of ureaand 67.5% by weight of H₂O are set in order to efficiently generate areducing reaction at the upstream side of the catalytic device 116without causing the urea solution to cake.

Accordingly, the urea of the urea solution in the urea tank can bemaintained to have a predetermined concentration. Consequently, the NOxin the exhaust gas can be greatly decreased by a reduction. Thus, thepresent invention can produce various remarkable and peculiar functionsand effects, which is very excellent.

1. An apparatus for identifying a concentration of a urea of a ureasolution, comprising: a urea concentration identifying chamber forcausing an identified urea solution introduced into a urea concentrationidentifying apparatus body to stay temporarily; a urea concentrationidentifying sensor heater provided in the urea concentration identifyingchamber; and a liquid temperature sensor provided in the ureaconcentration identifying chamber apart from the urea concentrationidentifying sensor heater at a constant interval; the urea concentrationidentifying sensor heater including a heater and an identifying liquidtemperature sensor provided in the vicinity of the heater, and theapparatus further comprising an identification control portion forapplying a pulse voltage to the urea concentration identifying sensorheater for a predetermined time, heating the identified urea solutionstaying temporarily in the urea concentration identifying chamber by theheater and identifying the concentration of the urea with a voltageoutput difference V0 corresponding to a temperature difference betweenan initial temperature and a peak temperature in the identifying liquidtemperature sensor.
 2. The apparatus for identifying a concentration ofa urea of a urea solution according to claim 1, wherein the voltageoutput difference V0 is equal to a voltage difference between an averageinitial voltage VI obtained by sampling an initial voltage beforeapplication of the pulse voltage at a predetermined number of times andan average peak voltage V2 obtained by sampling a peak voltage after theapplication of the pulse voltage at a predetermined number of times,that is,V 0=V 2−V
 1. 3. The apparatus for identifying a concentration of a ureaof a urea solution according to claim 1, wherein the identificationcontrol portion identifies a concentration of a urea of a urea solutionwith the voltage output difference V0 obtained for the identified ureasolution based on calibration curve data to be a correlation of avoltage output difference with a temperature for a predeterminedreference urea solution prestored in the identification control portion.4. The apparatus for identifying a concentration of a urea of a ureasolution according to claim 1, wherein the identification controlportion correlates a liquid type voltage output Vout for the voltageoutput difference V0 at a measuring temperature of the identified ureasolution with an output voltage for a voltage output difference at ameasuring temperature for a predetermined threshold reference ureasolution and thus carries out a correction.
 5. The apparatus foridentifying a concentration of a urea of a urea solution according toclaim 1, wherein the urea concentration identifying sensor heater is alaminated urea concentration identifying sensor heater in which a heaterand an identifying liquid temperature sensor are laminated through aninsulating layer.
 6. The apparatus for identifying a concentration of aurea of a urea solution according to claim 1, wherein the heater and theidentifying liquid temperature sensor in the urea concentrationidentifying sensor heater are constituted to come in contact with theidentified urea solution through a metallic fin, respectively.
 7. Theapparatus for identifying a concentration of a urea of a urea solutionaccording to claim 1, wherein the liquid temperature sensor isconstituted to come in contact with the identified urea solution throughthe metallic fin.
 8. A method for identifying a concentration of a ureaof a urea solution, comprising the steps of: applying a pulse voltagefor a predetermined time to a urea concentration identifying sensorheater including a heater and an identifying liquid temperature sensorprovided in the vicinity of the heater; heating an identified ureasolution by the heater; and identifying the concentration of the ureawith a voltage output difference V0 corresponding to a temperaturedifference between an initial temperature and a peak temperature in theidentifying liquid temperature sensor.
 9. The method for identifying aconcentration of a urea of a urea solution according to claim 8, whereinthe voltage output difference V0 is equal to a voltage differencebetween an average initial voltage V1 obtained by sampling an initialvoltage before application of the pulse voltage at a predeterminednumber of times and an average peak voltage V2 obtained by sampling apeak voltage after the application of the pulse voltage at apredetermined number of times, that is,V 0=V 2−V
 1. 10. The method for identifying a concentration of a urea ofa urea solution according to claim 8, wherein a concentration of a ureaof a urea solution is identified with the voltage output difference V0obtained for the identified urea solution based on calibration curvedata to be a correlation of a voltage output difference with atemperature for a predetermined reference urea solution which isprestored.
 11. The method for identifying a concentration of a urea of aurea solution according to claim 8, wherein a liquid type voltage outputVout for the voltage output difference V0 at a measuring temperature ofthe identified urea solution is correlated with an output voltage for avoltage output difference at a measuring temperature for a predeterminedthreshold reference urea solution and is thus corrected.
 12. The methodfor identifying a concentration of a urea of a urea solution accordingto claim 8, wherein the urea concentration identifying sensor heater isa laminated urea concentration identifying sensor heater in which aheater and an identifying liquid temperature sensor are laminatedthrough an insulating layer.
 13. The method for identifying aconcentration of a urea of a urea solution according to claim 8, whereinthe heater and the identifying liquid temperature sensor in the ureaconcentration identifying sensor heater are constituted to come incontact with the identified urea solution through a metallic fin,respectively.
 14. The method for identifying a concentration of a ureaof a urea solution according to claim 8, wherein the liquid temperaturesensor is constituted to come in contact with the identified ureasolution through the metallic fin.
 15. An apparatus for reducing anexhaust gas of a car, comprising: a urea solution supplying mechanismfor supplying a urea solution to an upstream side of a catalytic device,wherein the urea solution supplying mechanism is constituted by a ureasolution tank for storing the urea solution, a urea pump and a ureaspraying device for spraying the urea solution fed from the urea pump tothe upstream side of the catalytic device, and the apparatus foridentifying a concentration of a urea of a urea solution according toclaim 1 is provided in the urea tank or on an upstream side or adownstream side of the urea pump.
 16. A method for reducing an exhaustgas of a car, comprising the steps of: supplying a urea solution to anupstream side of a catalytic device through a urea solution supplyingmechanism constituted by a urea solution tank for storing the ureasolution, a urea pump and a urea spraying device for spraying the ureasolution fed from the urea pump onto the upstream side of the catalyticdevice, and identifying a concentration of a urea of the urea solutionin the urea tank or on an upstream side or a downstream side of the ureapump by using the method for identifying a concentration of a urea of aurea solution according to claim
 8. 17. The apparatus for identifying aconcentration of a urea of a urea solution according to claim 2, whereinthe identification control portion identifies a concentration of a ureaof a urea solution with the voltage output difference V0 obtained forthe identified urea solution based on calibration curve data to be acorrelation of a voltage output difference with a temperature for apredetermined reference urea solution prestored in the identificationcontrol portion.
 18. The apparatus for identifying a concentration of aurea of a urea solution according to claim 2, wherein the identificationcontrol portion correlates a liquid type voltage output Vout for thevoltage output difference V0 at a measuring temperature of theidentified urea solution with an output voltage for a voltage outputdifference at a measuring temperature for a predetermined thresholdreference urea solution and thus carries out a correction.
 19. Theapparatus for identifying a concentration of a urea of a urea solutionaccording to claim 3, wherein the identification control portioncorrelates a liquid type voltage output Vout for the voltage outputdifference V0 at a measuring temperature of the identified urea solutionwith an output voltage for a voltage output difference at a measuringtemperature for a predetermined threshold reference urea solution andthus carries out a correction.
 20. The apparatus for identifying aconcentration of a urea of a urea solution according to claim 2, whereinthe urea concentration identifying sensor heater is a laminated ureaconcentration identifying sensor heater in which a heater and anidentifying liquid temperature sensor are laminated through aninsulating layer.
 21. The apparatus for identifying a concentration of aurea of a urea solution according to claim 3, wherein the ureaconcentration identifying sensor heater is a laminated ureaconcentration identifying sensor heater in which a heater and anidentifying liquid temperature sensor are laminated through aninsulating layer.
 22. The apparatus for identifying a concentration of aurea of a urea solution according to claim 4, wherein the ureaconcentration identifying sensor heater is a laminated ureaconcentration identifying sensor heater in which a heater and anidentifying liquid temperature sensor are laminated through aninsulating layer.
 23. The apparatus for identifying a concentration of aurea of a urea solution according to claim 2, wherein the heater and theidentifying liquid temperature sensor in the urea concentrationidentifying sensor heater are constituted to come in contact with theidentified urea solution through a metallic fin, respectively.
 24. Theapparatus for identifying a concentration of a urea of a urea solutionaccording to claim 3, wherein the heater and the identifying liquidtemperature sensor in the urea concentration identifying sensor heaterare constituted to come in contact with the identified urea solutionthrough a metallic fin, respectively.
 25. The apparatus for identifyinga concentration of a urea of a urea solution according to claim 4,wherein the heater and the identifying liquid temperature sensor in theurea concentration identifying sensor heater are constituted to come incontact with the identified urea solution through a metallic fin,respectively.
 26. The apparatus for identifying a concentration of aurea of a urea solution according to claim 5, wherein the heater and theidentifying liquid temperature sensor in the urea concentrationidentifying sensor heater are constituted to come in contact with theidentified urea solution through a metallic fin, respectively.
 27. Theapparatus for identifying a concentration of a urea of a urea solutionaccording to claim 2, wherein the liquid temperature sensor isconstituted to come in contact with the identified urea solution throughthe metallic fin.
 28. The apparatus for identifying a concentration of aurea of a urea solution according to claim 3, wherein the liquidtemperature sensor is constituted to come in contact with the identifiedurea solution through the metallic fin.
 29. The apparatus foridentifying a concentration of a urea of a urea solution according toclaim 4, wherein the liquid temperature sensor is constituted to come incontact with the identified urea solution through the metallic fin. 30.The apparatus for identifying a concentration of a urea of a ureasolution according to claim 5, wherein the liquid temperature sensor isconstituted to come in contact with the identified urea solution throughthe metallic fin.
 31. The method for identifying a concentration of aurea of a urea solution according to claim 9, wherein a concentration ofa urea of a urea solution is identified with the voltage outputdifference V0 obtained for the identified urea solution based oncalibration curve data to be a correlation of a voltage outputdifference with a temperature for a predetermined reference ureasolution which is prestored.
 32. The method for identifying aconcentration of a urea of a urea solution according to claim 9, whereina liquid type voltage output Vout for the voltage output difference V0at a measuring temperature of the identified urea solution is correlatedwith an output voltage for a voltage output difference at a measuringtemperature for a predetermined threshold reference urea solution and isthus corrected.
 33. The method for identifying a concentration of a ureaof a urea solution according to claim 10, wherein a liquid type voltageoutput Vout for the voltage output difference V0 at a measuringtemperature of the identified urea solution is correlated with an outputvoltage for a voltage output difference at a measuring temperature for apredetermined threshold reference urea solution and is thus corrected.34. The method for identifying a concentration of a urea of a ureasolution according to claim 9, wherein the urea concentrationidentifying sensor heater is a laminated urea concentration identifyingsensor heater in which a heater and an identifying liquid temperaturesensor are laminated through an insulating layer.
 35. The method foridentifying a concentration of a urea of a urea solution according toclaim 10, wherein the urea concentration identifying sensor heater is alaminated urea concentration identifying sensor heater in which a heaterand an identifying liquid temperature sensor are laminated through aninsulating layer.
 36. The method for identifying a concentration of aurea of a urea solution according to claim 11, wherein the ureaconcentration identifying sensor heater is a laminated ureaconcentration identifying sensor heater in which a heater and anidentifying liquid temperature sensor are laminated through aninsulating layer.
 37. The method for identifying a concentration of aurea of a urea solution according to claim 10, wherein the heater andthe identifying liquid temperature sensor in the urea concentrationidentifying sensor heater are constituted to come in contact with theidentified urea solution through a metallic fin, respectively.
 38. Themethod for identifying a concentration of a urea of a urea solutionaccording to claim 11, wherein the heater and the identifying liquidtemperature sensor in the urea concentration identifying sensor heaterare constituted to come in contact with the identified urea solutionthrough a metallic fin, respectively.
 39. The method for identifying aconcentration of a urea of a urea solution according to claim 10,wherein the liquid temperature sensor is constituted to come in contactwith the identified urea solution through the metallic fin.
 40. Themethod for identifying a concentration of a urea of a urea solutionaccording to claim 11, wherein the liquid temperature sensor isconstituted to come in contact with the identified urea solution throughthe metallic fin.